- Email: [email protected]
Surfactant mediated TiO2 photoanodes and Cu2ZnSnS4 counter electrodes for high efficient dye sensitized solar cells
Journal Pre-proofs Surfactant Mediated TiO2 Photoanodes and Cu2ZnSnS4 Counter Electrodes for High Efficient Dye Sensitized Solar Cells Jitendra P. Sawant, Rohidas B. Kale PII: DOI: Reference:
S0167-577X(20)30112-9 https://doi.org/10.1016/j.matlet.2020.127407 MLBLUE 127407
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
27 December 2019 16 January 2020 21 January 2020
Please cite this article as: J.P. Sawant, R.B. Kale, Surfactant Mediated TiO2 Photoanodes and Cu2ZnSnS4 Counter Electrodes for High Efficient Dye Sensitized Solar Cells, Materials Letters (2020), doi: https://doi.org/10.1016/ j.matlet.2020.127407
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
© 2020 Published by Elsevier B.V.
Surfactant Mediated TiO2 Photoanodes and Cu2ZnSnS4 Counter Electrodes for High Efficient Dye Sensitized Solar Cells Jitendra P. Sawanta*, Rohidas B. Kaleb aDepartment bInstitute
of Physic, Mumbai University, Mumbai
of Science, Madam Cama Road, Fort, Mumbai-400032, India.
* Corresponding Author: E-mail: [email protected] (Jitendra P. Sawant) Abstract: Highly crystallized kesterite Cu2ZnSnS4 (CZTS) nanoparticles with an energy band gap of 1.54 eV and desired elemental compositions were prepared by hydrothermal method. CZTS thin films were prepared on titanium tetrachloride (TiCl4) treated fluorine doped tin oxide (FTO) substrate by doctor blade coating method. Morphological developments of hydrothermal synthesized, sodium dodecyl sulfate (SDS) mediated, TiO2 nanostructured thin films on TiCl4 treated FTO substrate were investigated. The CZTS/FTO counter electrodes (CSs) and TiO2 nanostructured photoanodes were employed in dye sensitized solar cells (DSSCs). DSSCs device with power conversion efficiency of 6.24% have been fabricated. The TiCl4 treated CZTS CEs and SDS mediated TiO2 nanostructure photoanodes provides suitable electrodes for low cost and high efficient dye sensitized solar cells. Keywords: Thin films, Nanocrystalline materials, Energy storage and conversion, CZTS counter electrode, Dye sensitized solar cell.
1
1 Introduction: Dye-sensitized solar cells (DSSCs) have drawn much attention because of simple fabrication process, and high solar to electric power conversion efficiency [1, 2]. A p- type kesterite phase Cu2ZnSnS4 has been proved to be promising CE material in dye sensitized solar cell [3]. With the advantage of low toxicity, earth abundance, high absorption coefficient and direct band gap of 1.55 eV [3], CZTS has regarded as promising material for photovoltaic applications. CZTS synthesized using hydrothermal and then doctor blade coated, drop casted or spin coated thin film electrodes, are the most used counter electrode in DSSCs [4]. Wide band gap semiconductor TiO2 is most promising photoanode in dye-sensitized solar cell [5]. Highly oriented nanostructured array of TiO2 photoanodes have shown excellent efficiency in dye-sensitized solar cell [6]. In present study, we report on hydrothermal synthesis of CZTS nanoparticles. Thin films of CZTS were deposited on titanium tetrachloride (TiCl4) treated FTO substrate using doctor blade coating method. Nanostructured TiO2 thin films were obtained by using sodium dodecyl sulfate (SDS) as a surfactant. N719 dye loaded TiO2 films as a photoanodes and CZTS counter electrodes were tested for DSSCs performance. The DSSCs fabricated showed the photoconversion efficiency of 6.26%. 2 Experimental Section: Cupric sulphate pentahydrate (CuSO4.5H2O), zinc sulphate (ZnSO4.7H2O), stannous chloride (SnCl2.2H2O), thiourea ((NH2)2)CS), Titanium isopropoxide (TTIP),Titanium tetrachloride (TiCl4), Sodium dodecyl sulfate (SDS), HCl (36%), ethyl cellulose, terpinoel, ethanol, N719 dye [Ditetrabutylammonium cis-bis (isothiocyanato) bis (2,2’- bipyrydil-4,4’dicarboxylato)] were purchased from S.D. Chem. Ltd. The procedure for hydrothermal synthesis of CZTS nanoparticles and CZTS thin films, is adopted from our earlier work [7]. However, FTO substrate used in this work were treated with 0.05 M aqueous solution of TiCl4 at 70 ºC for 30 min [8] and coated with CZTS paste [7] using doctor 2
blade method. TiO2 thin films were deposited on TiCl4 treated FTO substrate using hydrothermal method. 1 ml of (TTIP) in equal volume of distilled water and HCL (36%) were filled in autoclave (75 % capacity) and reaction is carried out at 180 ºC for 5 h. TiO2 thin films (named as S1, without SDS) were annealed at 400 ºC for 2 h. To study effect of SDS on morphology, TiO2 thin films were prepared by mixing 0.1 M (S2), 0.2 M (S3) and 0.3 M (S4) of SDS in the above solution maintaining other experimental conditions the same. Structural determination was carried using X-ray diffraction (XRD) spectrometer (XPERTPROMPD spectrometer). Raman spectrum was recorded with excitation source having wavelength 532 nm of He-Ne laser. The scanning electron microscopy (SEM, JEOL JSM-IT300) was used for morphological study. The optical absorption spectra were recorded using UV-Vis spectrometer (Perkin Elmer). The fabricated DSSCs devices (0.3 × 0.2 cm2) were tested for I - V characteristics using a solar simulator (100 mW/cm2) under (AM 1.5 G) conditions. 3 Results and Discussion: The XRD pattern of CZTS thin film exhibited strong diffraction peaks of (112), (200), (220) and (312) planes of kesterite phase CZTS (JCPDS card - 26-0575) (Fig.1(a)). The lattice parameters estimated a = 5.43 Å, b = 5.42 Å, c = 10.88 Å and average crystal size 17 nm matched well with earlier reported values [9]. Fig. 1(b) presents XRD pattern of TiO2 nanostructure thin film samples S1, S2, S3 and S4. The diffraction peaks attributed to planes (110), (101), (210), (220), (002) are consistent with the tetragonal rutile phase of TiO2 (JCPDS card - 01-82-0514), indicating the formation of single-phase TiO2 thin film [10]. The diffraction peak intensity of S2 sample is large, as compared to that of the other sample, indicating S2 is highly crystalline in nature. The energy band gap value of CZTS nanoparticles were estimated from the plot of (αhν)2 vs (hν) and was found to be 1.54 eV, which agrees with previous reports [3] (Fig. 1(c)). The estimated band gap value is near to the optimum value (1.51 eV) required for efficient photovoltaic solar conversion [8]. The energy band gap value for the TiO2 nanostructured thin films were estimated to be ~ 2.9 to 3.1 eV. [10] (Fig 1(d)). The possible binary, ternary phases of CZTS have similar XRD 3
pattern as that of CZTS [11]. Therefore, to identify CZTS phase, Raman spectra of CZTS nanoparticles was recorded and it exhibits three peaks at 287, 338 and 368 cm-1 position corresponds to pure phase CZTS as in agreement with earlier reports [12] (Fig. 1(e)). The SEM image of CZTS nanoparticles shows compact and solid CZTS microspheres of average diameters 1 - 4 µm (Fig S1(a)). The surface of doctor blade coated CZTS thin film is uniform, void free and consists of aggregated particles (Fig. S1(b)). From EDS analysis, atomic composition of Cu:Zn:Sn:S in the thin film sample were found to be 23.37:13.46:12.81:49.34 respectively, with the composition ratio Cu/(Zn+Sn) = 0.90 and Zn/Sn = 1.05. Fig. 2(a) depicts SEM image of S1 sample consisting of dense structure of TiO2 nanorods of ~ 250 nm diameter. The vertical grown rods covered with flower type nanorods and aligned nearly parallel to the substrate surface. Fig. 2(b) depicts the SEM image of the sample S2 prepared with 0.1 M of SDS surfactant. Three-dimensional compact flower like geometry is retained but shape of rods changed to highly pointed needle like structures and diameter is observed to be drastically decreased to ~ 150 nm. With further increase of SDS to 0.2 M (sample S3), density and diameter of nanorods decreased significantly and rods are seen more pointed away from the base as shown in Fig.2(c). After that nanoflowers disappeared significantly, and only diffused rods are visible on the surface of the substrate (Fig 2(d)). At sufficiently lower concentration, SDS promotes the ionic strength of the solution containing TTIP in water and HCl [10, 13], enhances the growth of rods and resulted in dense and uniform bunch of high crystalline TiO2 nanoflower like rods. The selected area electron diffraction pattern (SAED) showed CZTS nanoparticles are single crystalline in nature (Fig S2(a)). The interplanar spacing of CZTS (d112 = 0.318 nm) and TiO2 nanorods (d001=0.29 nm and d110= 0.32 nm) is consistent with the earlier reports [8, 10] (Fig S2(c, d)). The DSSCs, employing N719 dye on TiO2 nanostructure photoanodes (S1, S2, S3 and S4) and the CZTS counter electrode were prepared. The redox electrolyte containing 0.5 M LiI, 0.05 M I2 and 0.5 M tetrabutyl pyridine were introduced in sandwiched cell. Fig. 3(a) shows the current
4
density vs voltage curve of DSSCs measured under AM 1.5 G illuminations with light intensity of 100 mW2/cm2 and the solar cell parameters are summarized in the Table 1. The DSSCs employing S2, showed highest efficiency (6.24%) followed by S3, S1 and S4 photoanodes. The TiO2 nanostructured films with three-dimensional compact microflowers of small diameters facilitates increased light absorbing ability. This leads higher photogenerated current due to high recombination rate of the carrier at the FTO/TiO2 and electrolyte interface. In addition, due to relatively large density of nanorods the dye adsorption ability may have enhanced and may be the reasons for improved efficiency. The TiCl4 treatment on FTO resulted in uniform, continuous and highly mechanical stable CZTS thin films. This leads to the improvement in carrier transfer to the substrate [8]. The S3 and S4 TiO2 photoanode showed relatively low photoconversion
efficiencies, may be due to low density and compactness of nanorods which may have decreased the dye adsorption ability. Fig. 3(b) depicts the schematic representation of CZTS counter electrode and N719-(SDS) TiO2 working electrode in dye-sensitized solar cell with a possible electron transport mechanism. 4 Conclusion: CZTS nanoparticles and TiO2 nanostructured thin films were synthesized using conventional hydrothermal method. The CZTS nanoparticles exhibited spherical morphology, optimum elemental composition ratio and direct optical band gap of 1.54 eV. The morphological evolution of TiO2 nanorod thin films with sodium dodecyl sulfate (SDS) and without SDS were investigated. The correlation between morphology of TiO2 nanorod thin films and the power conversion efficiency in DSSCs ware investigated. The DSSCs employing the counter electrodes of CZTS deposited on TiCl4 treated FTO substrate, and photoelectrodes of SDS mediated TiO2 (S2) exhibited 6.24% of power conversion efficiency. The enhancement in efficiency may be attributed to improved carrier transfer to the substrate from continuous, uniform and highly mechanical stable CZTS counter electrodes after TiCl4 treatment. The highly oriented microflowers of TiO2 nanorods, may provide an effective 5
pathway for maximum dye adsorption leading to high-power conversion efficiency. Acknowledgement: This work is supported by the Department of Science and Technology, India under FISt (SR/FST/PSI173/2012) program. References: [1]
M. M. Byranvand, A. N. Kharat, M. H. Bazargan, Nano-Micro Lett. (2012), 4(4), 253.
[2]
M. Nazeeruddin, A. Kay, I. Rodicio, R. Humphry-Baker, E. Mueller, P. Liska, N. Vlachopoulos, M. Graetzel, J. Am. Chem. Soc. 1993, 115(14), 6382.
[3]
S. L. Chen, A. C. Xu, J. Tao, H. J. Tao, Y. Z. Shen, L. M. Zhu, J. J. Jiang, T. Wang, L. Pan, Green Chem. 2016, 8, 2793.
[4]
Z. Tong, Z. Su, F. Liu, L. Jiang, Y. Lia, J. Li, Y. Liu, Mater. Lett. 2014, 121, 241.
[5]
K. Fan, W. Zhang, T. Peng, J. Chen, F. Yang, J. Phys. Chem. C 2011, 115, 17213.
[6]
P. Roy, D. Kim, K. Lee, E. Spiecker, P. Schmuki, U. Bach, L. Schmidt-Mende, S. M. Zakeeruddin, A. Kay. M. K. Nazeeruddin, M. Gratzel, C. Kim, Nanoscale, 2010, 2, 45.
[7]
J. P. Sawant, R. B. Kale, Solid state electrochem.(2019) https://doi.org/10.1007/s10008-07904452-w.
[8]
S. Chen, A. Xu, J. Tao, H Tao, Y. Shen, L. Zhu, J. Jiang, T. Wang, L. Pan. ACS sustainable Chem. Eng. 2015, 3(11), 2652.
[9]
Y. B. Kishorkumar, P. UdayBhaskar, G. SureshBabu, V. Sundara Raja, Phys Status Solid A, 2010, 207, 149.
[10] K. P. Ghoderao, S. N. Jambhale, R. B. Kale, Superlattice and microstructures. 2018,124, 121. [11] J. Kong, Z. Zhou, M. Li, WH. Zhou, S.J. Yuan, R. Yao, Y. Zhao, S. Wu, Nanoscale Res. Let. 2013, 8, 464. [12] C. Zou, LJ. Zhang, DS. Lin, Y. Yang, Q. Li, XJ. Xu, X. Chen, SM. Huang, Crystengcomm 2011, 13, 3310.
6
[13] D. Wang, D. Choi, Z. Yang, V, Vishwanathan, Z. Nie, C. Wang, Y. Song, G Zang, J, Liu, Chem. Mat. 2008, 20, 3435. Table Captions: Table 1 Performance parameters of DSSCs fabricated using CZTS counter electrode and SDS mediated TiO2 photoelectrodes. Figure Captions: Fig. 1 a) XRD patter of CZTS thin film, b) XRD pattern of nanostructured TiO2 thin films, c & d) (αhν)2 vs (hν) plot for CZTS nanoparticles and TiO2 thin films e) Raman spectra of CZTS nanoparticles. Fig. 2 SEM images of TiO2 thin film, a) without SDS surfactant b) 0.1 M SDS, c) 0.2 M SDS and d) 0.3 M SDS. Fig. 3 a) Current density (Jsc) vs open circuit voltage (Voc) characteristics of DSSCs, b) Schematic representation of CZTS counter electrode and SDS mediated N719-TiO2 photoanode in dye sensitized solar cell.
Credit author statement Manuscript Title: Surfactant Mediated TiO2 Photoanodes and Cu2ZnSnS4 Counter Electrodes for High Efficient Dye Sensitized Solar Cells
Corresponding authors full Name: Jitendra Pandurang sawant ( [email protected]) Contributions of authors Author 1: Jitendra Pandurang Sawant 7
Carried out all the research work reported in the paper. Author 2: Dr. Rohidas Bhanudas Kale The present work is carried out under the supervision this author.
Regards, Jitendra P. Sawant
Author declaration:
1] No conflict of interest exists. We wish to confirm that there are no known conflicts of interest associated with this publication and there has been no significant financial support for this work that could have influenced its outcome. 2] Funding: No funding was received for this work. 3] We confirm that the manuscript has been read and approved by all named authors. 4] We confirm that the order of authors listed in the manuscript has been approved by all named authors.
Table 1 Performance parameters of DSSCs fabricated using CZTS counter electrode and SDS mediated TiO2 photoelectrodes. Sample
Jsc (mA/cm2)
Voc (Volts)
FF (%)
η (%)
S1
10.314
0.691
54
3.85
S2
13.253
0.763
61
6.24 8
S3
11.892
0.746
58
5.15
S4
9.346
0.689
53
3.42
Highlights
SDS mediated TiO2 photoanodes are prepared using hydrothermal method for DSSC.
CZTS/FTO counter electrode are prepared using hydrothermal method.
The DSSC device show 6.24% photoconversion efficiency.
9
10
11
12
S0167-577X(20)30112-9 https://doi.org/10.1016/j.matlet.2020.127407 MLBLUE 127407
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
27 December 2019 16 January 2020 21 January 2020
Please cite this article as: J.P. Sawant, R.B. Kale, Surfactant Mediated TiO2 Photoanodes and Cu2ZnSnS4 Counter Electrodes for High Efficient Dye Sensitized Solar Cells, Materials Letters (2020), doi: https://doi.org/10.1016/ j.matlet.2020.127407
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
© 2020 Published by Elsevier B.V.
Surfactant Mediated TiO2 Photoanodes and Cu2ZnSnS4 Counter Electrodes for High Efficient Dye Sensitized Solar Cells Jitendra P. Sawanta*, Rohidas B. Kaleb aDepartment bInstitute
of Physic, Mumbai University, Mumbai
of Science, Madam Cama Road, Fort, Mumbai-400032, India.
* Corresponding Author: E-mail: [email protected] (Jitendra P. Sawant) Abstract: Highly crystallized kesterite Cu2ZnSnS4 (CZTS) nanoparticles with an energy band gap of 1.54 eV and desired elemental compositions were prepared by hydrothermal method. CZTS thin films were prepared on titanium tetrachloride (TiCl4) treated fluorine doped tin oxide (FTO) substrate by doctor blade coating method. Morphological developments of hydrothermal synthesized, sodium dodecyl sulfate (SDS) mediated, TiO2 nanostructured thin films on TiCl4 treated FTO substrate were investigated. The CZTS/FTO counter electrodes (CSs) and TiO2 nanostructured photoanodes were employed in dye sensitized solar cells (DSSCs). DSSCs device with power conversion efficiency of 6.24% have been fabricated. The TiCl4 treated CZTS CEs and SDS mediated TiO2 nanostructure photoanodes provides suitable electrodes for low cost and high efficient dye sensitized solar cells. Keywords: Thin films, Nanocrystalline materials, Energy storage and conversion, CZTS counter electrode, Dye sensitized solar cell.
1
1 Introduction: Dye-sensitized solar cells (DSSCs) have drawn much attention because of simple fabrication process, and high solar to electric power conversion efficiency [1, 2]. A p- type kesterite phase Cu2ZnSnS4 has been proved to be promising CE material in dye sensitized solar cell [3]. With the advantage of low toxicity, earth abundance, high absorption coefficient and direct band gap of 1.55 eV [3], CZTS has regarded as promising material for photovoltaic applications. CZTS synthesized using hydrothermal and then doctor blade coated, drop casted or spin coated thin film electrodes, are the most used counter electrode in DSSCs [4]. Wide band gap semiconductor TiO2 is most promising photoanode in dye-sensitized solar cell [5]. Highly oriented nanostructured array of TiO2 photoanodes have shown excellent efficiency in dye-sensitized solar cell [6]. In present study, we report on hydrothermal synthesis of CZTS nanoparticles. Thin films of CZTS were deposited on titanium tetrachloride (TiCl4) treated FTO substrate using doctor blade coating method. Nanostructured TiO2 thin films were obtained by using sodium dodecyl sulfate (SDS) as a surfactant. N719 dye loaded TiO2 films as a photoanodes and CZTS counter electrodes were tested for DSSCs performance. The DSSCs fabricated showed the photoconversion efficiency of 6.26%. 2 Experimental Section: Cupric sulphate pentahydrate (CuSO4.5H2O), zinc sulphate (ZnSO4.7H2O), stannous chloride (SnCl2.2H2O), thiourea ((NH2)2)CS), Titanium isopropoxide (TTIP),Titanium tetrachloride (TiCl4), Sodium dodecyl sulfate (SDS), HCl (36%), ethyl cellulose, terpinoel, ethanol, N719 dye [Ditetrabutylammonium cis-bis (isothiocyanato) bis (2,2’- bipyrydil-4,4’dicarboxylato)] were purchased from S.D. Chem. Ltd. The procedure for hydrothermal synthesis of CZTS nanoparticles and CZTS thin films, is adopted from our earlier work [7]. However, FTO substrate used in this work were treated with 0.05 M aqueous solution of TiCl4 at 70 ºC for 30 min [8] and coated with CZTS paste [7] using doctor 2
blade method. TiO2 thin films were deposited on TiCl4 treated FTO substrate using hydrothermal method. 1 ml of (TTIP) in equal volume of distilled water and HCL (36%) were filled in autoclave (75 % capacity) and reaction is carried out at 180 ºC for 5 h. TiO2 thin films (named as S1, without SDS) were annealed at 400 ºC for 2 h. To study effect of SDS on morphology, TiO2 thin films were prepared by mixing 0.1 M (S2), 0.2 M (S3) and 0.3 M (S4) of SDS in the above solution maintaining other experimental conditions the same. Structural determination was carried using X-ray diffraction (XRD) spectrometer (XPERTPROMPD spectrometer). Raman spectrum was recorded with excitation source having wavelength 532 nm of He-Ne laser. The scanning electron microscopy (SEM, JEOL JSM-IT300) was used for morphological study. The optical absorption spectra were recorded using UV-Vis spectrometer (Perkin Elmer). The fabricated DSSCs devices (0.3 × 0.2 cm2) were tested for I - V characteristics using a solar simulator (100 mW/cm2) under (AM 1.5 G) conditions. 3 Results and Discussion: The XRD pattern of CZTS thin film exhibited strong diffraction peaks of (112), (200), (220) and (312) planes of kesterite phase CZTS (JCPDS card - 26-0575) (Fig.1(a)). The lattice parameters estimated a = 5.43 Å, b = 5.42 Å, c = 10.88 Å and average crystal size 17 nm matched well with earlier reported values [9]. Fig. 1(b) presents XRD pattern of TiO2 nanostructure thin film samples S1, S2, S3 and S4. The diffraction peaks attributed to planes (110), (101), (210), (220), (002) are consistent with the tetragonal rutile phase of TiO2 (JCPDS card - 01-82-0514), indicating the formation of single-phase TiO2 thin film [10]. The diffraction peak intensity of S2 sample is large, as compared to that of the other sample, indicating S2 is highly crystalline in nature. The energy band gap value of CZTS nanoparticles were estimated from the plot of (αhν)2 vs (hν) and was found to be 1.54 eV, which agrees with previous reports [3] (Fig. 1(c)). The estimated band gap value is near to the optimum value (1.51 eV) required for efficient photovoltaic solar conversion [8]. The energy band gap value for the TiO2 nanostructured thin films were estimated to be ~ 2.9 to 3.1 eV. [10] (Fig 1(d)). The possible binary, ternary phases of CZTS have similar XRD 3
pattern as that of CZTS [11]. Therefore, to identify CZTS phase, Raman spectra of CZTS nanoparticles was recorded and it exhibits three peaks at 287, 338 and 368 cm-1 position corresponds to pure phase CZTS as in agreement with earlier reports [12] (Fig. 1(e)). The SEM image of CZTS nanoparticles shows compact and solid CZTS microspheres of average diameters 1 - 4 µm (Fig S1(a)). The surface of doctor blade coated CZTS thin film is uniform, void free and consists of aggregated particles (Fig. S1(b)). From EDS analysis, atomic composition of Cu:Zn:Sn:S in the thin film sample were found to be 23.37:13.46:12.81:49.34 respectively, with the composition ratio Cu/(Zn+Sn) = 0.90 and Zn/Sn = 1.05. Fig. 2(a) depicts SEM image of S1 sample consisting of dense structure of TiO2 nanorods of ~ 250 nm diameter. The vertical grown rods covered with flower type nanorods and aligned nearly parallel to the substrate surface. Fig. 2(b) depicts the SEM image of the sample S2 prepared with 0.1 M of SDS surfactant. Three-dimensional compact flower like geometry is retained but shape of rods changed to highly pointed needle like structures and diameter is observed to be drastically decreased to ~ 150 nm. With further increase of SDS to 0.2 M (sample S3), density and diameter of nanorods decreased significantly and rods are seen more pointed away from the base as shown in Fig.2(c). After that nanoflowers disappeared significantly, and only diffused rods are visible on the surface of the substrate (Fig 2(d)). At sufficiently lower concentration, SDS promotes the ionic strength of the solution containing TTIP in water and HCl [10, 13], enhances the growth of rods and resulted in dense and uniform bunch of high crystalline TiO2 nanoflower like rods. The selected area electron diffraction pattern (SAED) showed CZTS nanoparticles are single crystalline in nature (Fig S2(a)). The interplanar spacing of CZTS (d112 = 0.318 nm) and TiO2 nanorods (d001=0.29 nm and d110= 0.32 nm) is consistent with the earlier reports [8, 10] (Fig S2(c, d)). The DSSCs, employing N719 dye on TiO2 nanostructure photoanodes (S1, S2, S3 and S4) and the CZTS counter electrode were prepared. The redox electrolyte containing 0.5 M LiI, 0.05 M I2 and 0.5 M tetrabutyl pyridine were introduced in sandwiched cell. Fig. 3(a) shows the current
4
density vs voltage curve of DSSCs measured under AM 1.5 G illuminations with light intensity of 100 mW2/cm2 and the solar cell parameters are summarized in the Table 1. The DSSCs employing S2, showed highest efficiency (6.24%) followed by S3, S1 and S4 photoanodes. The TiO2 nanostructured films with three-dimensional compact microflowers of small diameters facilitates increased light absorbing ability. This leads higher photogenerated current due to high recombination rate of the carrier at the FTO/TiO2 and electrolyte interface. In addition, due to relatively large density of nanorods the dye adsorption ability may have enhanced and may be the reasons for improved efficiency. The TiCl4 treatment on FTO resulted in uniform, continuous and highly mechanical stable CZTS thin films. This leads to the improvement in carrier transfer to the substrate [8]. The S3 and S4 TiO2 photoanode showed relatively low photoconversion
efficiencies, may be due to low density and compactness of nanorods which may have decreased the dye adsorption ability. Fig. 3(b) depicts the schematic representation of CZTS counter electrode and N719-(SDS) TiO2 working electrode in dye-sensitized solar cell with a possible electron transport mechanism. 4 Conclusion: CZTS nanoparticles and TiO2 nanostructured thin films were synthesized using conventional hydrothermal method. The CZTS nanoparticles exhibited spherical morphology, optimum elemental composition ratio and direct optical band gap of 1.54 eV. The morphological evolution of TiO2 nanorod thin films with sodium dodecyl sulfate (SDS) and without SDS were investigated. The correlation between morphology of TiO2 nanorod thin films and the power conversion efficiency in DSSCs ware investigated. The DSSCs employing the counter electrodes of CZTS deposited on TiCl4 treated FTO substrate, and photoelectrodes of SDS mediated TiO2 (S2) exhibited 6.24% of power conversion efficiency. The enhancement in efficiency may be attributed to improved carrier transfer to the substrate from continuous, uniform and highly mechanical stable CZTS counter electrodes after TiCl4 treatment. The highly oriented microflowers of TiO2 nanorods, may provide an effective 5
pathway for maximum dye adsorption leading to high-power conversion efficiency. Acknowledgement: This work is supported by the Department of Science and Technology, India under FISt (SR/FST/PSI173/2012) program. References: [1]
M. M. Byranvand, A. N. Kharat, M. H. Bazargan, Nano-Micro Lett. (2012), 4(4), 253.
[2]
M. Nazeeruddin, A. Kay, I. Rodicio, R. Humphry-Baker, E. Mueller, P. Liska, N. Vlachopoulos, M. Graetzel, J. Am. Chem. Soc. 1993, 115(14), 6382.
[3]
S. L. Chen, A. C. Xu, J. Tao, H. J. Tao, Y. Z. Shen, L. M. Zhu, J. J. Jiang, T. Wang, L. Pan, Green Chem. 2016, 8, 2793.
[4]
Z. Tong, Z. Su, F. Liu, L. Jiang, Y. Lia, J. Li, Y. Liu, Mater. Lett. 2014, 121, 241.
[5]
K. Fan, W. Zhang, T. Peng, J. Chen, F. Yang, J. Phys. Chem. C 2011, 115, 17213.
[6]
P. Roy, D. Kim, K. Lee, E. Spiecker, P. Schmuki, U. Bach, L. Schmidt-Mende, S. M. Zakeeruddin, A. Kay. M. K. Nazeeruddin, M. Gratzel, C. Kim, Nanoscale, 2010, 2, 45.
[7]
J. P. Sawant, R. B. Kale, Solid state electrochem.(2019) https://doi.org/10.1007/s10008-07904452-w.
[8]
S. Chen, A. Xu, J. Tao, H Tao, Y. Shen, L. Zhu, J. Jiang, T. Wang, L. Pan. ACS sustainable Chem. Eng. 2015, 3(11), 2652.
[9]
Y. B. Kishorkumar, P. UdayBhaskar, G. SureshBabu, V. Sundara Raja, Phys Status Solid A, 2010, 207, 149.
[10] K. P. Ghoderao, S. N. Jambhale, R. B. Kale, Superlattice and microstructures. 2018,124, 121. [11] J. Kong, Z. Zhou, M. Li, WH. Zhou, S.J. Yuan, R. Yao, Y. Zhao, S. Wu, Nanoscale Res. Let. 2013, 8, 464. [12] C. Zou, LJ. Zhang, DS. Lin, Y. Yang, Q. Li, XJ. Xu, X. Chen, SM. Huang, Crystengcomm 2011, 13, 3310.
6
[13] D. Wang, D. Choi, Z. Yang, V, Vishwanathan, Z. Nie, C. Wang, Y. Song, G Zang, J, Liu, Chem. Mat. 2008, 20, 3435. Table Captions: Table 1 Performance parameters of DSSCs fabricated using CZTS counter electrode and SDS mediated TiO2 photoelectrodes. Figure Captions: Fig. 1 a) XRD patter of CZTS thin film, b) XRD pattern of nanostructured TiO2 thin films, c & d) (αhν)2 vs (hν) plot for CZTS nanoparticles and TiO2 thin films e) Raman spectra of CZTS nanoparticles. Fig. 2 SEM images of TiO2 thin film, a) without SDS surfactant b) 0.1 M SDS, c) 0.2 M SDS and d) 0.3 M SDS. Fig. 3 a) Current density (Jsc) vs open circuit voltage (Voc) characteristics of DSSCs, b) Schematic representation of CZTS counter electrode and SDS mediated N719-TiO2 photoanode in dye sensitized solar cell.
Credit author statement Manuscript Title: Surfactant Mediated TiO2 Photoanodes and Cu2ZnSnS4 Counter Electrodes for High Efficient Dye Sensitized Solar Cells
Corresponding authors full Name: Jitendra Pandurang sawant ( [email protected]) Contributions of authors Author 1: Jitendra Pandurang Sawant 7
Carried out all the research work reported in the paper. Author 2: Dr. Rohidas Bhanudas Kale The present work is carried out under the supervision this author.
Regards, Jitendra P. Sawant
Author declaration:
1] No conflict of interest exists. We wish to confirm that there are no known conflicts of interest associated with this publication and there has been no significant financial support for this work that could have influenced its outcome. 2] Funding: No funding was received for this work. 3] We confirm that the manuscript has been read and approved by all named authors. 4] We confirm that the order of authors listed in the manuscript has been approved by all named authors.
Table 1 Performance parameters of DSSCs fabricated using CZTS counter electrode and SDS mediated TiO2 photoelectrodes. Sample
Jsc (mA/cm2)
Voc (Volts)
FF (%)
η (%)
S1
10.314
0.691
54
3.85
S2
13.253
0.763
61
6.24 8
S3
11.892
0.746
58
5.15
S4
9.346
0.689
53
3.42
Highlights
SDS mediated TiO2 photoanodes are prepared using hydrothermal method for DSSC.
CZTS/FTO counter electrode are prepared using hydrothermal method.
The DSSC device show 6.24% photoconversion efficiency.
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